There has been proposed a seat for a vehicle, of which a seatback portion of a backseat is tilted (retractable type), and/or which is detachable from a vehicle floor (detachable type), so as to reduce level difference on the vehicle floor inside the vehicle for effectively using a space inside the vehicle. Regarding such retractable type seat and detachable type seat, for example, the seat is secured on the vehicle floor, or at a side surface of the vehicle compartment, so as not to generate backlash when the seat is in a locked state. Therefore, when the seat is in the locked state, ride quality is not negatively affected. Further, the seat is rigidly structured so that the locked state may not be released by a large shock.
A lock apparatus of a seat, which includes a base secured at a lower portion of a seat (movable member) and a striker secured to a vehicle floor (fixed member), is disclosed in US7044552B1 (hereinafter, referred to as reference 1). A first groove portion is formed at the base so that the striker is engaged into the first groove portion. The striker is surrounded by an inner end of the first groove portion of the base and a side surface (rear side surface) of a second groove portion formed at a hook which is pivotably supported to the base, thereby shifting the seat apparatus to a locked state and securing the seat to the vehicle floor. In order to surround the striker by the first groove portion of the base and the second groove portion of the hook without backlash at the locked state of the lock apparatus, a load is applied on a cam member, which is pivotably supported to the base, by means of a spring applying biasing force in a direction for pressing the hook. Further, in addition to the cam member, a pawl is further employed for preventing a pivotal movement of the hook in a case where external force is applied to the striker in a direction to be away from the first groove portion of the base (second groove portion of the hook) when the lock apparatus is in the locked state.
As described above, according to the reference 1, the backlash is restrained by the cam member, and the resistance to the external force is reinforced by the pawl. Thus, the backlash of the lock apparatus in the locked state is restrained. In addition, the locked state of the lock apparatus is restrained from being released due to large shock (large impact), for example.
According to the lock apparatus disclosed in the reference 1, a rotational shaft of the cam member and a rotational shaft of the pawl are arranged to be coaxial. Further, the rotational shafts of the pawl and the cam member and a rotational shaft of the hook are arranged at one side relative to the striker to which the external force is applied. Therefore, in a case where the external force is applied to the striker in a direction towards an opening of the first portion (i.e., in a direction where the striker exits the first groove portion of the base and the second groove portion of the hook), the lock apparatus may not be strong enough to resist such external force because the cam member, the pawl and the hook are supported only at one side relative to the striker to resist such external force.
Further, the larger a length between the rotational shaft of the cam member and a surface (portion) thereof for contacting the hook is, the greater the efficiency for restraining the backlash becomes. Still further, the shorter a length between the rotational shaft of the pawl and a surface (portion) thereof for contacting the hook is, the greater the strength of the lock apparatus becomes. However, according to the lock apparatus disclosed in the reference 1, the rotational shafts of the pawl and the cam member are coaxially arranged, as described above. Therefore, in a case where the length from the cam member (pawl) to the hook is arranged to be larger so as to increase a performance for restraining the backlash, a performance for resisting the external force may be reduced. On the other hand, in a case where the length between from the pawl (cam member) to the hook is arranged to be smaller so as to increase the performance for resisting the external force, the backlash may not be restrained sufficiently.
Still further, because the cam member and the pawl are arranged coaxial, the cam member and the pawl are arranged to overlap with each other in a thickness direction of such components. In other words, centers of the hook and the cam member in the thickness direction thereof deviate, and further centers of the hook and the pawl in the thickness direction thereof deviate. Therefore, load for restraining the backlash and the external force applied to the striker are received at a position dislocated from the centers of the hook in the thickness direction. Accordingly, torsion moment is generated to the rotational shaft of the hook, and the performance of the cam member and the pawl may not be exerted for restraining the backlash and for resisting the external force.
A need thus exists for a lock apparatus of a seat for a vehicle, which is not susceptible to the drawback mentioned above.